Method of applying cadium-free incandescent lamp powder coating

ABSTRACT

Disclosed is a method for applying a yellow incandescent bugfoiler pigment coating comprising a fine-ground blend of praseodymium doped zirconium silicate and silica. This cadmium-free blend is preferably applied electrostatically in three coats to the interior of a bulb to diffuse the light and block the emitted UV wavelengths. The color of the blend will intensify with increasing heat and return to it&#39;s initial yellow color upon cooling.

FIELD OF THE INVENTION

The present invention is directed to incandescent lamps, particularly tolamps commonly referred to as "bug lights" or "bugfoilers." These lampstraditionally contain a coating containing cadmium, which acts to blockthe UV emitted from the source, thereby reducing the attraction of bugsto the lamp. In the present invention the bugfoiler powder comprises afinely ground compound of praseodymium-doped zirconium silicate andsilica. This cadmium-free blend is applied electrostatically in aplurality of coats (e.g., three) to the interior of the bulb to diffusethe light and block UV wavelengths. The color of the blend intensifieswith increasing heat and then returns to it's initial color uponcooling.

BACKGROUND OF THE INVENTION

The pigments presently used for some yellow colorants and"Bugfoiler"(i.e., bug light) applications contain cadmium in one or moreof several forms including: powder, slurry and/or as a ceramic glaze.

For example, in Canadian Patent No. 1,181,469 (General Electric) thereis disclosed a bug light coating comprising (a) light refractiveparticles; (b) a selective light-absorbing particulant colorant; and (c)flux calcined diatomaceous SiO.sub. 2. The preferred light reflectiveparticles are Al.sub. 2O.sub. 3, SiO.sub. 2, Al.sub. 2O.sub. 3-SiO.sub.2 and/or CaCO.sub. 3. The preferred colorant is CdS. This compositionaffords a decorative and functional "yellow" bug light.

While the prior art bug lights are effective, the cadmium employedtherein (e.g., CdS, etc.) is considered a carcinogen (see, Fourth AnnualReoort on Carcinoqens, NTP 85-002, 1985, p. 48; and Merck Index, 11thed., No. 1611, p. 245 (1989)) and a hazardous waste material. Therefore,continued and/or repeated disposal and usage of cadmium in suchapplications is costly and no longer acceptable throughout the industry.

SUMMARY OF THE INVENTION

The present invention is directed to an improved, cadmium-freeincandescent bugfoiler lamp having coated on its inner surface, a powderconsisting of a fine ground compound of praseodymium doped zirconiumsilicate and silica. The present invention also includes a method ofapplying this cadmium-free blend preferably electrostatically to theinterior of a bulb to diffuse light and block UV wavelengths.

The compositional blend of the present invention has been found to be acost effective replacement for previously used cadmium containingformulations, first because of the cost of the ingredients used andsecond due to its simple manufacturing process. In addition, thecomposition is not carcinogenic and therefore problems such as operatorsafety and waste disposal are either sharply diminished, or eliminatedby the use of this composition in comparison with the prior artcompositions containing cadmium.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The major pigment constituent of the composition of the presentinvention is commercially available from O. Hommel Co. (as YE-494 YellowPigment) and Ferro Corporation, Color Division (as C-146 YellowPigment). These two yellow pigments consist of zirconium oxide dopedwith praseodymium, denoted by:

    ZrSiO.sub. 4/Pr

For further information on such pigments, see, U.S. Pat. No. 3,847,639,the disclosure of which is hereby incorporated herein by reference, aswell as West German Patent No. 1,905,673.

In investigating the potential use of this yellow pigment as asubstitute for cadmium-containing materials in bug lights, it was foundthat the ZrSiO.sub. 4/Pr pigment would not consistently adhereelectrostatically to incandescent lamp walls. Thus, efforts were made toidentify a compositional blend which would improve the adherence of thepigment. These efforts included:

(1) Matching particle size to amorphous silica size by dry/wet grinding.Silica particle sizes from about 2 to 10 microns (average particle size)were studied. The wet grinding method generally resulted in a poorcoating. Thus, all material were dry-ground to either about 4 micronaverage particle size or about 2.8 microns. The 4 micron averageparticle size was deemed preferable because the smaller particle sizegenerally made the pigment whiter than optimally desired.

(2) Amorphous Silica - PPG Lo-Vel 27 was added to the pigment at variouslevels to improve the adherence characteristics. Blends of pigment with50, 30, 20, 10, 5 and 2% of silica added to increase adherence andflowability were studied. While all levels of added silica improvedpigment adherence, as the percentage of added silica increased, thecolor of the pigment became whiter, but the overall yellow color didremain. The most preferred level of added amorphous silica wasdetermined to be about 10% (by weight). While amorphous silica was foundto be preferred, other forms of silica are believed to be capable ofsubstitution herein for the amorphous silica, e.g., hydrophobic and/orhydrophilic silicas, calcined diatomaceous silicas, and the like, hereincollectively referred to as "silica."

(3) Also tested was a combination of the yellow pigment with boric acid(in powder form) to improve adherence. While the boric acid (from about1 to 5 wt. %) improves adherence, it can decrease the life of thefinished lamp if not heated above 800° F.

Finally, it was discovered that in use (i.e., in the illuminated bulb)the pigment changes color (from yellow to orange) with the increasingtemperature of the bulb wall, but after use, the pigment returns to itsoriginal yellow color once the bulb cools down. This is not believed tobe a problem since the consumer purchasing a yellow "bug light" gets ayellow bug light.

As determined from the above discussed tests and research, the currentlypreferred embodiment for a cadmium-free pigment coating for incandescentbug lamps comprises an electrostatically deposited homogeneous blend of:

a) ZrSiO.sub. 4/Pr yellow pigment, fine dry-ground to an averageparticle size of about 4 microns [as determined by light scatteringlaser diffraction]; and

b) 10% amorphous silica, advantageously PPG Lo-Vel 27.

The cadmium-free blend of the present invention is advantageouslyapplied uniformly to the interior surface of the incandescent bulb usingan electrostatic deposition process. Such processes are well known inthe lamp industry, and are widely varied among the manufacturers oflamps. It is believed that any of the known electrostatic processes maybe employed to provide the present coating.

For reference purposes regarding electrostatic deposition of lampcoatings, see inter alia, U.S. Pat. No. 4,914,346 (Ingraham), U.S. Pat.No. 4,806,824 (Paynter, et al.), U.S. Pat. No. 4,597,984 (Jansma), U.S.Pat. No. 4,499,397 (James), U.S. Pat. No. 4,441,047 (Collins, et al.),U.S. Pat. No. 4,441,046 (James), U.S. Pat. No. 4,421,803 (Czeiler, etal.), U.S. Pat. No. 4,099,080 (Dawson, et al.), U.S. Pat. No. 4,081,709(Collins, et al.), U.S. Pat. No. 3,928,668 (Snow), U.S. Pat. No.2,921,827 (Meister, et al.), and U.S. Pat. No. 2,811,131 (Lopenski etal.), the disclosures of which are hereby incorporated herein byreference.

The pigment blend of the present invention can be coated in single ormulti-layers (i.e., greater than two), in either heavy coats or lightcoats, as desired by the skilled artisan and the particular requirementsof the lamp in which the coating is to be applied. It has beendiscovered that the preferred bug light coating of the present inventionis most advantageously formed as three individually and uniformlyapplied coats.

The preferred tripartite coating used herein consists of two initialcoating layers of the above described cadium-free pigment blend, thefirst of which is applied at an average weight (average of grams perlayer per A-19 bulb) of about 0.1072 (±0.0399) grams, and the secondlayer of which is applied at an average weight of about 0.2946 (±0.0978)grams. The final layer of silica is applied at an average weight ofabout 0.0478 (±0.0423) grams, to aid in the adherence of the entirecoating to the bulb wall. All three layers preferably used hereinaverage about 0.5012 ±0.2038 grams per finished envelope (A-19).

Alternatively, a very thin coating of silica can be applied first to theinterior surface of the bulb, with the thin pigment coating appliedthereover. Likewise, an initial thin coating of the pigment may beprotected with a thin overcoat of silica.

It will also be appreciated that other lamp additives such as, otherpigments (e.g., for other colors, etc.), and other additives such assynthetic amorphous silicon dioxide hydrate, titanium dioxide, zincoxide, aluminum oxide, synthetic amorphous silica, surface treated withhydrocarbon-type wax, fumed and calcined silica, calcined diatomaceousearth and/or silica, and the like, at levels ranging from about 1 wt.percent to about 50 wt. percent may be employed herein for whateveradvantages and attributes desired by those of ordinary skill in thisart. It likewise will be appreciated however, that such additives maychange the flowability, adherence, and the agglomeration properties ofthe final product, and that modifications in either layering, and/orapplication procedures may need adjustment to compensate therefor.Likewise, if envelopes other than A-19 are employed, adjustments will benecessary in the amounts of materials required.

The present invention has been described in detail, including thepreferred embodiments thereof. However, it will be appreciated thatthose skilled in the art, upon consideration of the present disclosure,may make modifications and/or improvements on this invention and stillbe within the scope and spirit of this invention as set forth in thefollowing claims.

What is claimed is:
 1. A method of manufacturing yellow incandescent buglights comprising electrostatically coating the interior surface ofincandescent lamps with a cadmiumfree yellow pigment comprising a dryground homogeneous blend of:a) about 90 percent by weight ZrSiO.sub.4/Pr yellow pigment, fine-dry ground to an average particle size ofabout 4 microns; and b) about 10 percent by weight amorphous silica. 2.A method of manufacturing yellow incandescent bug lights comprisingelectrostatically coating th interior surface of incandescent lamps witha cadmiumfree yellow pigment comprising a dry ground homogeneous blendof:a) about 90 percent by weight ZrSiO.sub. 4/Pr yellow pigment,fine-dry ground to an average particle size of about 2.8 microns; and b)about 10 percent by weight amorphous silica.
 3. The method fo claim 1 or2, which further comprises electrostatically applying at least twolayers of the pigment coating to the interior surface of the lamps. 4.The method of claim 1 or 2, which further comprises electrostaticallydepositing a final coating of amorphous silica over the two pigmentlayers.